I have a 383 stroker, carbureted, running off the stock fuel pump (brand new) ran to a fuel pressure regulator. Sitting at around 6lbs of fuel at idle. The problem I am having is that the oil pressure will gradually drop from about 55psi down to around 10psi after the car is ran for a little while and everything is up to operating temperature. I am not sure why oil pressure would drop since the oil pump, engine, fuel pump, pretty much everything is brand new. What is considered a "low" oil pressure that would warrant worrying?

 

Cam bearings?

 

It's a brand new engine with only 45 miles on it. I dont think the bearings are bad because it was professionally assembled.

 

gauge? was entire engine degunked? something clogged like an oil passage? just guessin

 

Your first step should be to verify actual oil pressure with a known-quality mechanical gauge from under the hood. If idle oil pressure is actually that low; there's a problem.

BTW, Just because something is new---or was 'professionally assembled'---doesn't always mean it's okay.

 

I would suspect loose-ish bearing clearances. What weight oil are you running? 55 to 10 is a pretty big drop. How much is oil pressure increasing with RPM? It's never this simple, but the "rule of thumb" is about 10 PSI per 1000 RPM (which is a gross oversimplification, but it gets the idea across).

 

10 PSI/1000 RPM is a minimum but the oil pump can only put out so much pressure.

When oil gets hot, it flows much easier. Pressure is a resistance to flow. Bearing clearances are a restriction. Lets say your main bearings are set for 0.003". Cold oil will have a hard time going through that clearance and pressure will be high. As the oil gets hot, it flows like water through that clearance and pressure is low.

Main bearings don't cause noise but will fail if they don't get proper lubrication. Rod bearings , when they fail, will create a knocking sound. Cam bearings are like main bearings and will not make a sound when they fail.

Since you have good pressure when the oil is cold but pressure drops off when hot, I don't think you have a faulty gauge however installing a mechanical gauge is a good way to confirm the reading.

Buy a new oil filter and put it on the engine. Cut open the old filter. Take out a section of filter material and squish it in a vise to squeeze the oil out of it. Open up the filter material and look for contamination. Any bearing that's failing will leave material in the filter.

There's also the possibility that bearing clearances are incorrect. Maybe the crankshaft mains were machined down and standard bearings were installed? Clearances not checked and are excessive.

Since it was Professionally assembled, check on warranty coverage. Are you sure the cam bearings were replaced? A new engine should not have low oil pressure like that.

 

UPDATE: Changed the oil and filter and now the oil never drops below 15psi. To think that's all she needed... thanks for the help yall!

 

Faulty bypass in the filter, maybe?

 

Did you use the same viscosity oil and what brand filter did you use prior and now?

 

I AGREE.

 

I apologize for never returning to this thread! I used a used a WIX 51069 oil filter (same filter I replaced it with) with Royal Purple engine break-in oil 10W-30 (PN#11487) (also the same oil I replaced the old with).
If there are any knowledgable recommendations for healthy oil type to use with this kind of engine, since we are on the subject anyways, I would appreciate any advice. (12:1 compression ratio, 383 stroker with <100 miles on it still). Sincerely thank you for all the help guys.

 

With pressure that low I would be running at least a 40 if not a 50 weight to get the pressure up a bit. 15 at hot idle is still low. Generally a factory high performance SBC would be 25-30 at hot idle.

GD

 

I've had a mech. gauge on my GTA. Typically its about 70-80psi cold, and 15-20psi cold.

My daily driver on the other hand is about 7psi hot, and thats the way Ford likes it. My 2013 Focus ST was the same way. Scared the crap out of me though because I had never had a Direct Injection car, and the injector ticks sound EXACTLY like lifter tick from low oil pressure.